Stomatal development in leaves is negatively regulated by receptor-like proteins {TOO MANY MOUTHS; hereinafter, referred to as “TMM”} and ERECTA family receptor-like kinases (ER, ERL1 and ERL2) (for example, see Non Patent Literatures 1 and 2).
Two possible ligands which bind to these receptors, EPIDERMAL PATTERNING FACTOR (hereinafter, referred to as “EPF”) 1 and EPF2, act as negative signaling factors at distinct steps during stomatal development (for example, see Non Patent Literatures 3 to 5). In addition, another negative regulator (STOMATAL DENSITY AND DISTRIBUTION 1; hereinafter, referred to as “SDD1”), which is a subtilisin-type proteinase, is reported to be dependent on TMM to function (for example, see Non Patent Literature 6).